Non-volatile memory

Is there a component that provides a single bit of non-volatile memory? I'm looking for a way to flag an array of removable, disposable items as being new or spent. The value only needs to be set once (so something like an intentionally blown fuse would work), but it needs to be small, disposably cheap, and preserve state without power.

Staff: Mentor

Something like a tamper sensor? Seems like you could do it with some conductive thing that gets mechanically broken. The fuse you mention would be good, and is commonly used if you have power available. You can also use a latching relay, which maintains the state when power is removed.

Welcome to PF, Hookt.
There are a lot of different ways to approach this. It would be helpful to know what sort of physical constraints are involved (size, attachment method, physical ruggedness, etc.) in order to home in on an appropriate one.

My thought is for automating some small chemical tests, perhaps 6 or so at time. An ideal solution (pardon the pun) is the size of a playing card, give or take. Smaller is better; it needs to fit in one's hand.

The tests would be mounted on a removable, disposable tray. The tray would be replaced as a single unit, but each test on the tray would need its own new/spent flag.

The trays will likely be plastic (as they'll be disposable). The flag components would be physically attached to the tray, and make an electrical contact with a reader circuit when the tray is inserted.

The flag components shouldn't be fragile, but there's no extreme ruggedness requirement. A tray might accidentally fall from a table, but won't be run over by a tank (ordinarily).

I've been thinking about this and I'm wondering if you could use some sort of tape that would change colors when exposed to a light source/laser or electrical current. Then use optical techniques to read the change.

Staff: Mentor

I've been thinking about this and I'm wondering if you could use some sort of tape that would change colors when exposed to a light source/laser or electrical current. Then use optical techniques to read the change.

Hey, I like the idea of using light to read the change. A spring-loaded thing could pop when the tray is removed, and the moved position of whatever popped could be read using a reflective photosensor: